Genetic analyses of atypical Toxoplasma gondii strains reveal a fourth clonal lineage in North America

Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
International journal for parasitology (Impact Factor: 3.87). 02/2011; 41(6):645-55. DOI: 10.1016/j.ijpara.2011.01.005
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Toxoplasma gondii is a widespread parasite of animals that causes zoonotic infections in humans. Previous studies have revealed a strongly clonal population structure in North America and Europe, while strains from South America are genetically separate and more diverse. However, the composition within North America has been questioned by recent descriptions of genetically more variable strains from this region. Here, we examined an expanded set of isolates using sequenced-based phylogenetic and population analyses to re-evaluate the population structure of T. gondii in North America. Our findings reveal that isolates previously defined by atypical restriction fragment length polymorphism patterns fall into two discrete groups. In one case, these new isolates represent variants of an existing lineage, from which they differ only by minor mutational drift. However, in the second case, it is evident that these isolates define a completely new lineage that is common in North America. Support for this new lineage was based on phylogeny, principle components analysis, STRUCTURE analyses, and statistical analysis of gene flow between groups. This new group, referred to as haplogroup 12, contains divergent genotypes previously referred to as A and X, isolated from sea otters. Consistent with this, group 12 was found primarily in wild animals, as well as occasionally in humans. This new lineage also has a highly clonal population structure. Analysis of the inheritance of multilocus genotypes revealed that different strains within group 12 are the products of a single recombination event between type 2 and a unique parental lineage. Collectively, the archetypal type 2 has been associated with clonal expansion of a small number of lineages in the North, as a consequence of separate but infrequent genetic crosses with several different parental lines.

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Available from: Chunlei Su, Oct 02, 2015
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    • "These genotypes were deposited into the public database in ToxoDB and therefore designated as ToxoDB PCR-RFLP genotypes. Among these genotypes , a fourth clonal lineage (Type 12, its designation derived from haplogroup 12) in North America was recently recognized (Khan et al. 2011). This lineage consists of ToxoDB genotypes #4 and #5 (Shwab et al. 2014). "
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    ABSTRACT: Toxoplasma gondii infects virtually all warm-blooded hosts worldwide. Recently, attention has been focused on the genetic diversity of the parasite to explain its pathogenicity in different hosts. It has been hypothesized that interaction between feral and domestic cycles of T. gondii may increase unusual genotypes in domestic cats and facilitate transmission of potentially more pathogenic genotypes to humans, domestic animals, and wildlife. In the present study, we tested black bear (Ursus americanus), bobcat (Felis rufus), and feral cat (Felis catus) from the state of Pennsylvania for T. gondii infection. Antibodies to T. gondii were found in 32 (84.2%) of 38 bears, both bobcats, and 2 of 3 feral cats tested by the modified agglutination test (cut off titer 1:25). Hearts from seropositive animals were bioassayed in mice, and viable T. gondii was isolated from 3 of 32 bears, 2 of 2 bobcats, and 2 of 3 feral cats. DNA isolated from culture-derived tachyzoites of these isolates was characterized using multilocus PCR-RFLP markers. Three genotypes were revealed, including ToxoDB PCR-RFLP genotype #1 or #3 (Type II, 1 isolate), #5 (Type 12, 3 isolates), and #216 (3 isolates), adding to the evidence of genetic diversity of T. gondii in wildlife in Pennsylvania. Pathogenicity of 3 T. gondii isolates (all #216, 1 from bear, and 2 from feral cat) was determined in outbred Swiss Webster mice; all three were virulent causing 100% mortality. Results indicated that highly mouse pathogenic strains of T. gondii are circulating in wildlife, and these strains may pose risk to infect human through consuming of game meat. This article is protected by copyright. All rights reserved.
    Journal of Eukaryotic Microbiology 11/2014; DOI:10.1111/jeu.12196 · 3.22 Impact Factor
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    • "A new concept of congenital human toxoplasmosis Previously we believed there are only three major genotypes of Toxoplasma gondii that are responsible for congenital infections and remaining isolates are harmless (Ndir et al. 2004). This belief is changing because of greater genetic diversity as a result of sexual recombination of the parasite (Su et al. 2010; Khan et al. 2011). A recent study indicated that congenital T. gondii can occur in immune mothers (seropositive) when an atypical genotype overcomes the acquired resistance from the original infecting genotype (Elbez-Rubinstein et al. 2009). "
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    ABSTRACT: Abstract The epidemiology of toxoplasmosis in pregnancy is a major issue for public health. Primary infection in pregnant women can lead to serious sequelae. This review examined current sero-epidemiology and risks factor data for Toxoplasma gondii in pregnant women in Arab and African countries. A systematic electronic search of published literature was conducted. Data were extracted from relevant studies. Seropositivity is high in both regions. African countries have higher seropositivity than Arab countries due to differences in risk factors. Data on T. gondii infection in pregnancy are scant in many countries, especially where there is lack of political stability. Identified risk factors included eating raw meat, proximity with cats, undercooked food, and increasing maternal age. Toxoplasmosis in pregnancy in Arab and African countries is an underestimated health problem. Further research is needed. This report is a foundation for strategies and policies for intervention needed to combat the consequences of congenital toxoplasmosis.
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    • "T. gondii has a clonal population structure. While in Europe and North America three clonal types (clonal type I, II and III) dominate, non-canonical clonal lineages and other genotypes are predominantly found in South America, Africa and Asia (Khan et al., 2009, 2011). Their virulence phenotypes have been determined in mice. "
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